1. Field of the Invention
The present invention relates, in general, to centrifugal blowers used for moving air by accelerating it radially outward within an impeller to a surrounding casing of scroll shape and, more particularly, to a centrifugal blower provided with an eddy blade in an air outlet port of the casing to generate a uniform current velocity distribution of air, and thereby prevent generation of an eddy at variance with a main current in a stream of air.
2. Description of the Prior Art
As well known to those skilled in the art, centrifugal blowers are machines in which air is sucked into an impeller in an axial direction, and is accelerated radially within the impeller to a surrounding casing of scroll shape to be discharged from the casing in a direction perpendicular to the air inlet direction. The centrifugal blowers are preferably used as machines for feeding air under constant pressure.
A conventional centrifugal blower is shown in FIG. 1. As shown in the drawing, the centrifugal blower comprises a multiblade impeller 4 with a plurality of blades arranged around a rotor, and a scroll casing 6 surrounding the multiblade impeller 4, with a spiral passage defined between the scroll casing 6 and the impeller 4 to guide air radially accelerated in the impeller 4 to an air outlet port of the scroll casing, thus discharging the air from the scroll casing 6 through the air outlet port.
An air inlet port (not shown) is formed at the scroll casing 6 in an axial direction of the impeller 4, and the air outlet port 8 is formed at the casing 6 such that the outlet port 8 is perpendicular to the air inlet port.
In the operation of the centrifugal blower, air is sucked into the impeller 4 through the air inlet port due to a suction force generated by a rotation of the impeller 4, and is accelerated radially in the impeller 4 to the scroll casing 6. In such a case, due to the scroll shape of the casing 6, air under constant pressure is discharged from the casing 6 through the air outlet port 8.
However, when the flow rate of outlet air from the centrifugal blower exceeds a predetermined reference level, a velocity gradient of air flowing in the outlet port 8 is generated, so that an eddy at variance with a main current in a stream of air is generated. The eddy substantially reduces blower efficiency, and produces operating noise of the blower.
That is, air flowing in the outlet port 8 has a nonuniform current velocity distribution V such that the air current velocity is gradually increased in proportion to the distance from the center of the impeller 4, as shown by the arrows of FIG. 2. Therefore, a clockwise eddy E at variance with the main current in the stream of air is generated in the outlet port 8. The nonuniform current velocity distribution V of air and the clockwise eddy reduce the flow rate of air, thus reducing the blower efficiency and generating operating noise of the blower.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a centrifugal blower with an eddy blade, in which the eddy blade prevents generation of an eddy in the air outlet port of a scroll casing, thus enhancing blower efficiency and reducing operating noise of the blower.
In order to accomplish the above objects, the present invention provides a centrifugal blower, comprising a multiblade impeller with a plurality of blades arranged around a rotor, and a scroll casing surrounding the multiblade impeller, with a spiral passage defined between the scroll casing and the impeller to guide air radially accelerated in the impeller to an air outlet port of the scroll casing, thus discharging the air from the scroll casing through the air outlet port, further comprising an eddy blade installed in the spiral passage at a position around the air outlet port to generate a uniform current velocity distribution of air, thus preventing generation of an eddy at variance with a main current in a stream of air, wherein the eddy blade is placed in the spiral passage such that leading and trailing edges thereof are directed toward an interior and the air outlet port of the scroll casing, respectively, and the eddy blade is inclined downward from the leading edge to the trailing edge at a predetermined angle of inclination xcex2 relative to a horizontal axis.
In the centrifugal blower, the angle of inclination xcex2 of the eddy blade is preferably set to 13xc2x0xcx9c25xc2x0.
The leading and trailing edges of the eddy blade are preferably rounded forward and rearward in vertical directions at predetermined radiuses of curvature (R1, R2).
The radius of curvature (R1) of the leading edge, the radius of curvature (R2) of the trailing edge, and a distance (C) between centers of curvature of the leading and trailing edges are preferably expressed as follows:
R1=(0.08xcx9c0.1)xc3x97(D2xe2x88x92D1)/4
R2=(0.03xcx9c0.05)xc3x97(D2xe2x88x92D1)/4
C=(0.95xcx9c1.01)xc3x97(D2xe2x88x92D1)/2
where D1 is an inner diameter of the impeller equal to a diameter of the rotor, and D2 is an outer diameter of the impeller including the blades.
The eddy blade, placed in the spiral passage of the scroll casing, is preferably rounded upward in a latitudinal direction at a lower surface thereof at a predetermined radius of curvature (R3), and is preferably rounded upward in the latitudinal direction at an upper surface thereof at another predetermined radius of curvature (R4).
The radiuses of curvature (R3, R4) of the lower and upper surfaces are preferably expressed as follows:
R3=1.2D1
R4=(0.7xcx9c0.9)D1
where D1 is the inner diameter of the impeller equal to the diameter of the rotor.